Resin parts such as an instrumental panel, a console box or door trim are generally composed of a substrate made of a hard resin and a skin mounted on a surface of the substrate. Structurally, resin parts are classified into three major types: a "fully-padded type" having the skin mounted fully across a surface of the substrate; a "half-padded type" in which part of the substrate is exposed and part covered with skin; and a "padless type" which is solely composed of substrate.
Particularly, an instrument panel of the "half-padded type" is extensively used on low-price cars and is shown in FIGS. 12 (Prior Art) and 13 (Prior Art) indicated by reference numeral 51. The substrate 52 of the instrument panel 51 is required to have certain properties such as a specified rigidity and formability. To meet these requirements, the substrate is chiefly formed of ABS (acrylonitrile-butadiene-styrene), PP (polypropylene), etc. The elastic sheet (skin) 53 comprises a cushion layer 54 typically made of a soft polyurethane foam, an insert 55 (optional) buried under the cushion layer 54 and made of a resin or an iron plate, and a skin layer 56 made of PVC (polyvinyl chloride).
The instrument panel 51 may typically be fabricated by the following procedure. First, the substrate 52 is formed by a known injection molding technique. A surface of a separately vacuum-formed elastic sheet 53 is heated by means of a heater or the like. Then, the substrate 52 is set up in a vacuum forming mold, with a surface of the substrate having been coated with a primer, an adhesive and any other desired agents for pre-treatment. Thereafter, the preheated elastic sheet 53 is placed above and in alignment with the substrate 52 as shown in FIG. 14 and the two members are bonded together.
A problem with this approach is that the substrate 52 and the elastic sheet 53 have to be formed separately and subsequently bonded together. To accomplish this, it has been necessary to provide separate steps and molds for forming the substrate 52 and the elastic sheet 53. A further problem is that the need to apply the primer and adhesive adds to the number of overall steps involved. There has thus been a strong need to improve the efficiency of automotive instrument panel production while reducing the production cost.